Endothermic gas atmosphere and 80Ni soft magnetic materials heat treatment

[marcus4]

Hi guys. I wonder is it possible to use endothermic gas instead of hydrogen atmosphere for 80Ni soft magnetic materials heat treatment? Any disandvantages?

 

[EdStainless]

What is your endo composition?
If it is hydrogen rich and very low dew point then it should work.
Most endo gas isn't dry enough for this application.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[marcus4]

Hi Edstainless. Endo gas composition is : H2 33%, Co23%, Co2 0,3%, Ch4 0,5%, H2O 0,6%, rest N2. Dew point is 0c.

Btw, what are the disadvantages of the higher dew point than recommended (-50c)?

 

[EdStainless]

There is a risk of oxidation and carburization in endo gas.
At your dew point oxidation is a sure thing. You are OK at annealing temp, but as you cool the metal will oxidize.
You might get away with -40, but nothing higher.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[marcus4]

Thanks EdStainless, I understand. I have no problem with thin oxide layer since the parts are transformer laminations but carburization is something else. I'm not sure is that going to affect magnetics properties of the final part???

 

[MagBen]

yes, dew point needs to be -40C (F) or better. both carburization and oxidation will degrade magentics. note the main reason to use dry H2 is to prevent oxidation and remove C, S etc.
Forming a thin oxide layer is one way of decreasing eddy current, but should be in a controllable manner.

 

[marcus4]

Thanks MagBen. Happy New Year. I understand that Endo gas will cause some magnetics degradation but unfortunately I have no appropriate HT service in my region. That's why I ask this dumb question. Of course, I can experiment and find it myself but this kind of material is not cheap enough to do that. Now, when I know what to expect from Endo gas I wonder about one more thing. Will the Endo gas change the chemical composition of the material or it will form just the top oxid layer? I ask it because of possibility to repeat the process under the H2 atmosphere if the Endo give me low permeability results.

 

[MagBen]

Marcus, Happy new year to you too. I cannot answer your question, but if you cannot use pure dry H2, you may try vacuum (better than 10^-3 torr) in a leak-free furnace, or in a dry Ar atomosphere, still, a samll sacrifice in magnetics is expected.

 

[marcus4]

Thanks MagBen. It seems that I will have to search better for this kind of service. This requirements are not so usual in my region.